Hydrogen exchange methods developed in this laboratory are being used to study structure and structure change in some biologically interesting macromolecular systems. Individual changes that occur in hemoglobin upon binding of ligands are being studied. The free energy associated with each change can be measured. The same methods are being used to study structure and structure change in some membrane-protein systems - in rhodopsin disk membranes, in sarcoplasmic vesicles, and also in myelin and red cell membranes. In poly-nucleotides, chemical pathways for hydrogen exchange and the dynamic breathing behavior of these polymers are being studied.